How do you strum when palm muting?
It is possible to strum upwards while muting. Try to find a comfortable area that doesn't compromise the sound of your strings, but also doesn't leave them too...well.. not muted. Just try strumming up with your palm on the bridge to begin with, and then you'll be able to strum up while muting.
Is Palm muting hard?
The technique is much used in funk and disco too, but it's often combined with fret-hand muting, so it can be hard to hear which hand is creating the effect. “Plenty to listen to then.